1. Field of the Invention
The present invention relates to the aircraft instrumental landing system (ILS) sector and to the so-called glide path (GP) systems and i.e. to guiding aircraft glide.
2. Description of the Prior Art
Within conventional GP systems, an antenna which emits signals is used, installed within the airport in close proximity to the landing runway, from which aircraft obtains information regarding the progress of descent manoeuvres and, in particular, regarding the angle of inclination with respect to the horizon of the path followed by the aircraft.
GP systems which use the irradiation of two particular signals are known, the characteristics of which (usable frequencies, modulation type and the antenna radiation patterns) are, for many aspects, fixed by international regulations. Such signals, emitted in order to guide the descent or glide are: a “carrier plus side band” (CSB) signal, and a “side band only” (SBO) signal.
Typically, the antenna system used is made up of an array of two or three radiating elements, each of which emits a CSB or SBO signal in such a manner that, together with the signals reflected from the ground, the irradiated signals produce the two desired CSB and SBO signal irradiation patterns.
Normally, the CSB and SBO signals are generated by a suitable transmitter connected to a distribution device or unit which splits the signal power and shifts the phase of the signals generated, in such a manner as to be able to supply parts of the SSB and SBO signals, having pre-defined phases and amplitudes, to each radiating element of the array.
The Applicant has noted that the conventional GP systems have performances which are strongly dependent on the presence or absence of reflecting obstacles within the area of installation of such a system, and on the characteristics of the ground in front of the antenna (slope, rugosity etc.). That makes the choice of the site in which to install the antenna, which will, however, have to be in close proximity to the landing runway, particularly problematic.